The invention relates to compounds useful in treating conditions associated with calcium channel function. More specifically, the invention concerns compounds containing benzhydril and 6-membered heterocyclic moieties that are useful in treatment of conditions such as stroke and pain.
Native calcium channels have been classified by their electrophysiological and pharmacological properties as T, L, N, P and Q types (for reviews see McCleskey, E. W. et al. Curr Topics Membr (1991) 39:295-326, and Dunlap, K. et al. Trends Neurosci (1995) 18:89-98). T-type (or low voltage-activated) channels describe a broad class of molecules that transiently activate at negative potentials and are highly sensitive to changes in resting potential. The L, N, P and Q-type channels activate at more positive potentials (high voltage activated) and display diverse kinetics and voltage-dependent properties. There is some overlap in biophysical properties of the high voltage-activated channels, consequently pharmacological profiles are useful to further distinguish them. L-type channels are sensitive to dihydropyridine agonists and antagonists, N-type channels are blocked by the Conus geographus peptide toxin, xcfx89-conotoxin GVIA, and P-type channels are blocked by the peptide xcfx89-agatoxin IVA from the venom of the funnel web spider, Agelenopsis aperta. A fourth type of high voltage-activated calcium channel (Q-type) has been described, although whether the Q- and P-type channels are distinct molecular entities is controversial (Sather, W. A. et al. Neuron (1995) 11:291-303; Stea, A. et al. Proc Natl Acad Sci USA (1994) 91:10576-10580; Bourinet, E. et al. Nature Neuroscience (1999) 2:407-415). Several types of calcium conductances do not fall neatly into any of the above categories and there is variability of properties even within a category suggesting that additional calcium channels subtypes remain to be classified.
Biochemical analyses show that neuronal high voltage activated calcium channels are heterooligomeric complexes consisting of three distinct subunits (xcex11, xcex12xcex4 and xcex2) (reviewed by De Waard, M. et al. Ion Channels (1997) vol. 4, Narahashi, T. ed. Plenum Press, NY). The xcex11 subunit is the major pore-forming subunit and contains the voltage sensor and binding sites for calcium channel antagonists. The mainly extracellular xcex12 is disulfide-linked to the transmembrane xcex4 subunit and both are derived from the same gene and are proteolytically cleaved in vivo. The xcex2 subunit is a nonglycosylated, hydrophilic protein with a high affinity of binding to a cytoplasmic region of the xcex11 subunit. A fourth subunit, xcex3, is unique to L-type calcium channels expressed in skeletal muscle T-tubules. The isolation and characterization of xcex3-subunit-encoding cDNAs is described in U.S. Pat. No. 5,386,025 which is incorporated herein by reference.
Recently, each of these xcex11 subtypes has been cloned and expressed, thus permitting more extensive pharmacological studies. These channels have been designated xcex11A-xcex11I and xcex11S and correlated with the subtypes set forth above. xcex11A channels are of the P/Q type; xcex11B represents N; xcex11C, xcex1xe2x80x21D, xcex11F and xcex11S represent L; xcex11E represents a novel type of calcium conductance, and xcex11G-xcex11I represent members of the T-type family, reviewed in Stea, A. et al. in Handbook of Receptors and Channels (1994), North, R. A. ed. CRC Press; Perez-Reyes, et al. Nature (1998) 391:896-900; Cribbs, L. L. et al. Circulation Research (1998) 83:103-109; Lee, J. H. et al. Journal of Neuroscience (1999) 19:1912-1921.
Further details concerning the function of N-type channels, which are synaptic channels, have been disclosed, for example, in U.S. Pat. No. 5,623,051, the disclosure of which is incorporated herein by reference. As described, N-type channels possess a site for binding syntaxin, a protein anchored in the presynaptic membrane. Blocking this interaction also blocks the presynaptic response to calcium influx. Thus, compounds that block the interaction between syntaxin and this binding site would be useful in neural protection and analgesia. Such compounds have the added advantage of enhanced specificity for presynaptic calcium channel effects.
U.S. Pat. No. 5,646,149 describes calcium channel antagonists of the formula A-Y-B wherein B contains a piperazine or piperidine ring directly linked to Y. An essential component of these molecules is represented by A, which must be an antioxidant; the piperazine or piperidine itself is said to be important. The exemplified compounds contain a benzhydril substituent, based on known calcium channel blockers (see below). U.S. Pat. No. 5,703,071 discloses compounds said to be useful in treating ischemic diseases. A mandatory portion of the molecule is a tropolone residue; among the substituents permitted are piperazine derivatives, including their benzhydril derivatives. U.S. Pat. No. 5,428,038 discloses compounds which are said to exert a neural protective and antiallergic effect. These compounds are coumarin derivatives which may include derivatives of piperazine and other six-membered heterocycles. A permitted substituent on the heterocycle is diphenylhydroxymethyl. Thus, approaches in the art for various indications which may involve calcium channel blocking activity have employed compounds which incidentally contain piperidine or piperazine moieties substituted with benzhydril but mandate additional substituents to maintain functionality.
Certain compounds containing both benzhydril moieties and piperidine or piperazine are known to be calcium channel antagonists and neuroleptic drugs. For example, Gould, R. J. et al. Proc Natl Acad Sci USA (1983) 80:5122-5125 describes antischizophrenic neuroleptic drugs such as lidoflazine, fluspirilene, pimozide, clopimozide, and penfluridol. It has also been shown that fluspirilene binds to sites on L-type calcium channels (King, V. K. et al. J Biol Chem (1989) 264:5633-5641) as well as blocking N-type calcium current (Grantham, C. J. et al. Brit J Pharmacol (1944) 111:483-488). In addition, Lomerizine, developed by Kanebo KK, is a known non-specific calcium channel blocker. A review of publications concerning Lomerizine is found in Dooley, D., Current Opinion in CPNS Investigational Drugs (1999) 1:116-125.
U.S. application Ser. No. 09/401,699 filed Sep. 23, 1999 and incorporated herein by reference discloses benzhydril-substituted piperidines and piperazines which block calcium channels, especially N-type channels.
The present invention is based on the recognition that compounds comprising a six-membered heterocyclic ring containing at least one nitrogen coupled to two hydrophobic clusters (each cluster coupled optionally through a linker) provide calcium channel blocking activity. Thus these compounds are particularly useful for treating stroke and pain. By focusing on these moieties, compounds useful in treating indications associated with excessive calcium channel activity and combinatorial libraries that contain these compounds can be prepared.
The invention relates to compounds useful in treating conditions such as stroke, migraine, chronic neuropathic and acute pain, epilepsy, hypertension, cardiac arrhythmias, and other indications associated with calcium metabolism, including synaptic calcium channel-mediated functions. The compounds of the invention are derivatives of piperidine or piperazine linked to hydrophobic substituents which enhance the calcium channel blocking activity. Thus, in one aspect, the invention is directed to therapeutic methods that employ compounds of the formulas 
wherein each Z is independently N or CH, but one Z must be N;
wherein n1 is 1 and n is 0 or 1;
X1 and X2 are linkers;
Ar represents one or two substituted or unsubstituted aromatic or heteroaromatic rings, and
Cy represents one or two substituted or unsubstituted aliphatic cyclic or heterocyclic rings, or consists of one substituted or unsubstituted aliphatic cyclic or heterocyclic ring and one substituted or unsubstituted aromatic or heteroaromatic ring;
each of Ya and Yb is two substituted or unsubstituted aromatic or heteroaromatic rings, or can be two substituted or unsubstituted aliphatic cyclic or heterocyclic rings or consists of one substituted or unsubstituted aliphatic cyclic or heterocyclic ring and one substituted or unsubstituted aromatic or heteroaromatic ring;
with the proviso that said rings cannot both be phenyl when both Ar includes a single phenyl ring and X1 contains less than 5C;
and with the proviso that formula (1b) must contain at least one aromatic or heteroaromatic ring;
11 is 0 or 1;
R1 is substituted or unsubstituted alkyl (1-6C), substituted or unsubstituted aryl (6-10C) or substituted or unsubstituted arylalkyl (7-16C) optionally containing 1-4 heteroatoms selected from the group consisting of halo, N, P, O, and S or may independently be halo, OR, SR, NR2, OOCR, NROCR, COR, COOR, CONR2, CF3, CN or NO2, wherein R is H or alkyl (1-6C). Substituents included in Ya, Yb, Ar and Cy are also selected from the foregoing.
The invention is directed to methods to antagonize calcium channel activity using the compounds of formulas (1a) or (1b) and thus to treat associated conditions. It will be noted that the conditions may be associated with abnormal calcium channel activity, or the subject may have normal calcium channel function which nevertheless results in an undesirable physical or metabolic state that can be benefited by lowering calcium transport. In another aspect, the invention is directed to pharmaceutical compositions containing these compounds.
The invention is also directed to combinatorial libraries containing the compounds of formulas (1a) or (1b) and to methods to screen these libraries for members containing particularly potent calcium channel blocking activity including blocking activity for channels of a particular type.
The compounds of formulas (1a) or (1b), useful in the methods of the invention, exert their desirable effects through their ability to antagonize the activity of calcium channels, including those which are synaptic in their activity. While the compounds of formulas (1a) or (1b) generally have this activity, the availability of a multiplicity of calcium channel blockers permits a nuanced selection of compounds for particular disorders. Thus, the availability of this class of compounds provides not only a genus of general utility in indications that are affected by excessive calcium channel activity, but also provides a large number of compounds which can be mined and manipulated for specific interaction with particular forms of calcium channels. The availability of recombinantly produced calcium channels of the xcex11A-xcex11I and xcex11S types set forth above, facilitates this selection process. Dubel, S. J. et al. Proc Natl Acad Sci USA (1992) 89:5058-5062; Fujita, Y. et al. Neuron (1993) 10:585-598; Mikami, A. et al. Nature (1989) 340:230-233; Mori, Y. et al. Nature (1991) 350:398-402; Snutch, T. P. et al. Neuron (1991) 7:45-57; Soong, T. W. et al. Science (1993) 260:1133-1136; Tomlinson, W. J. et al Neuropharmacology (1993) 32:1117-1126; Williams, M. E. et al. Neuron (1992) 8:71-84; Williams, M. E. et al. Science (1992) 257:389-395; Perez-Reyes, et al. Nature (1998) 391:896-900; Cribbs, L. L. et al. Circulation Research (1998) 83:103-109; Lee, J. H. et al. Journal of Neuroscience (1999) 19:1912-1921.
Thus, while it is known that calcium channel activity is involved in a multiplicity of disorders, the types of channels associated with particular conditions is the subject of ongoing data collection. The association of N-type channels in conditions associated with neural transmission would indicate that compounds of the invention which target N-type receptors are most useful in these conditions. Most of the members of the genus of compounds of formulas (1a) or (1b) target N-type channels; other members of the genus may target other channels; many members of the genus target channels of several types.
There are two distinguishable types of calcium channel inhibition. The first, designated xe2x80x9copen channel blockage,xe2x80x9d is conveniently demonstrated when displayed calcium channels are maintained at an artificially negative resting potential of 3 about xe2x88x92100 mV (as distinguished from the typical endogenous resting maintained potential of about xe2x88x9270 mV). When the displayed channels are abruptly depolarized under these conditions, calcium ions are caused to flow through the channel and exhibit a peak current flow which then decays. Open channel blocking inhibitors diminish the current exhibited at the peak flow and can also accelerate the rate of current decay.
This type of inhibition is distinguished from a second type of block, referred to herein as xe2x80x9cinactivation inhibition.xe2x80x9d When maintained at less negative resting potentials, such as the physiologically important potential of xe2x88x9270 mV, a certain percentage of the channels may undergo conformational change, rendering them incapable of being activatedxe2x80x94i.e., openedxe2x80x94by the abrupt depolarization. Thus, the peak current due to calcium ion flow will be diminished not because the open channel is blocked, but because some of the channels are unavailable for opening (inactivated). xe2x80x9cInactivationxe2x80x9d type inhibitors increase the percentage of channels that are in an inactivated state.
Among the conditions associated in which blocking calcium transport would be of therapeutic value are stroke, head trauma, epilepsy, and chronic, neuropathic and acute pain. Calcium transport, especially that associated with N-type channels, is also implicated in other neurological disorders such as migraine, epilepsy, mood disorders, schizophrenia, and certain degenerative disorders. Other conditions that benefit from reduced calcium flux include depression, anxiety, and other psychoses. Cardiovascular conditions benefited include hypertension and cardiac arrhythmias.
The availability of the libraries containing the compounds of formulas (1a) or (1b) also provides a source of compounds which may be screened for activity with regard to the various ion channels. The various types of ion channels are associated with conditions that are susceptible to treatment. Blockers of sodium channels, for example, are useful as local anesthetics, and in treating cardiac arrhythmias, as anticonvulsants, and in treating hyperkalemic periodic paralysis. Potassium channel blockers are useful in treating hypertension and cardiac arrhythmias; various other receptors are associated with psychoses, schizophrenia, depression, and apnea. Thus, the library of compounds of the invention is useful in standard screening techniques as a source of effective pharmaceutical compounds.
Synthesis
The compounds of the invention may be synthesized using conventional methods. Illustrative of such methods are the following schemes.
The piperazine derivatives of the invention are prepared conveniently by synthetic routes wherein one of the linkers, X1 or X2, is supplied as a carboxylic acid or carboxylic acid derivative and is coupled to piperazine already bound to the remaining substituent. Thus, in general, these compounds are prepared by Reaction Scheme 1 illustrated below for the embodiment wherein Ar is benzhydril and Ya(X1)n1 is depicted as R. 
The intermediate amide product can be reduced as shown, if desired, using a suitable reducing agent. Preferably, the reducing agent is BH3 if R represents phenyl or benzyl, or is LAH if R contains a xcfx80-bond other than in an aromatic system, such as the instance wherein R is xe2x80x94CH2CHxe2x95x90CHxcfx86. Alternatively, the piperazine ring nitrogen shown coupled to R is protected with t-butyl carbonate (BOC) which can then be removed and replaced with a different substituent as shown in Reaction Scheme 2 and then reduced, for example, with BH3. 
In the foregoing reaction schemes, EDC represents ethyldicyclohexylcarbodiimide, LAH represents lithium aluminum hydride, TFA is trifluoroacetic acid.
Some of the desired carboxylates are commercially available including instances which include cyclic aliphatics. Where they are not, they can be prepared by a Wittig reaction and reduced as desired, as shown in Reaction Scheme 3, which illustrates preparation of the benzhydril embodiment using benzophenone. However, phenylcyclohexylketone or dicyclohexylketone can be substituted for benzophenone to obtain the corresponding embodiments wherein the substituent coupled to linker is symbolized by Cy in formula (1b). 
In this reaction scheme, LiHMDS represents lithium hexamethyl disilazide. The reaction proceeds smoothly with benzophenone and phenylcyclohexylketone; use of dicyclohexylketone results in an aberrant molecular weight as measured by mass spectrometry, but nevertheless provides product.
The reagents in the above-referenced scheme may or may not contain substitutions on the aromatic or cyclic aliphatic moieties. For example, compounds in the bis-4-fluorophenyl butylidine series are commercially available and Reaction Scheme 4 illustrates the preparation of these compounds. 
The compounds of the invention that are piperidine derivatives are prepared in an analogous manner, as shown in Reaction Scheme 5 using the illustration where Ar represents benzhydril. 
As shown, the 4-piperidone is reacted with the corresponding carboxylic acid derivative of benzhydril and then subjected to reductive amination. R, then, represents Ya and may include a portion of the linker, X1, which linker includes CH2NH.
In general, the synthesis of the compounds of the invention is conventional and employs techniques generally known in the art.
The compounds of formulas (1a) or (1b) are defined as shown in terms of the embodiments of their various substituents:
each Z is independently N or CH, but one Z must be N.
R1 is alkyl (1-6C) aryl (6-10C) or arylalkyl (7-16C) optionally containing 1-4 heteroatoms selected from the group consisting of N, P, O, S, and halo. R1 may also be the xe2x80x9csubstituentsxe2x80x9d halo, OR, SR, NR2, OOCR, NROCR, COR, COOR, CONR2, CF3, CN or NO2, wherein R is H or alkyl (1-6C). These xe2x80x9csubstituentsxe2x80x9d may also be present on the alkyl, aryl or arylalkyl moieties contained in Formulas 1a and 1b; aryl groups may also contain alkyl substituents. Preferred embodiments of R1 include phenyl, phenylalkyl, F, Cl, Br, I, CF3, OR, NR2 and alkyl. Particularly preferred are F, OMe, NH2, NMe2, NHOAc, CONH2, Br, COOEt, and COOMe, as well as methyl. Preferably, however, 11 is 0.
As n2 may be 0 or 1, X2 may be present or not. X1 and X2 are suitable linkers containing 1-10C which may be saturated or unsaturated and may contain a ring. The linker may also contain one or two heteroatoms selected from N, O and S and may be substituted with the xe2x80x9csubstituentsxe2x80x9d listed above. Preferred embodiments of X2 include xe2x80x94(CH2)axe2x80x94 wherein a is 1-10, preferably 1-6, xe2x80x94(CH2)bCOxe2x80x94, where b is 1-9, and xe2x80x94(CH2)cCHxe2x95x90CH, where c is 0-4. Also preferred for X2 is xe2x80x94NH(CH2)dxe2x80x94 where d is 1-6, when the coupled Z is CH.
Thus, formulas (1a) and (1b) are similar, except that compounds of formula (1a) contain more mandated aromatic substituents linked to the heterocyclic 6-membered ring and those of (1b) contain more aliphatic cyclic or heterocyclic moieties. In each case, when X2 is present, X2 represents a linker which spaces the Ar or Cy moiety from Z preferably at a distance of 3-20 xc3x85, and may contain at least one heteroatom which is nitrogen or oxygen. Included in such linkers are amines and carbonyl functionalities, including amides. The linker may also be unsaturated or may be an alkylene group. Typically, X2 is (CH2)1-8 or xe2x80x94NH(CH2)1-6xe2x80x94 or (CH2)0-5, or xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)0-3xe2x80x94 or xe2x80x94CO(CH2)1-8xe2x80x94. Similarly, X1 spaces the Ya or Yb from the nitrogen of the heterocyclic ring at a distance of 3-20 xc3x85.
In both cases, when linked to two aromatic or heterocyclic or other cyclic moieties, as is always the case for Ya and Yb, X1 or X2 must accommodate this and a typical embodiment is xe2x80x94(CH2)0-6xe2x80x94CHxe2x80x94CH(CH2)0-6CO, or xe2x80x94CH(CH2)0-7. X1 or X2 may also contain a xcfx80-bond, e.g., xe2x80x94(CH2)0-5CHxe2x95x90C, thus providing sufficient valence to couple two ring systems or Cxe2x95x90CH(CH2)0-5xe2x80x94.
In preferred forms of formulas (1a) and (1b), X2 is (CH2)1-8, (CH2)1-5CO(CH2)0-3, (CH2)1-5NH(CH2)0-3, (CH2)0-5CONH(CH2)0-3, xe2x80x94(CH2)0-5CHxe2x95x90CH(CH2)0-3xe2x80x94 and (CH2)1-5NHCO(CH2)0-3, with accommodation as required for two rings. Preferred for X1 are CH(CH2)1-10 and CH(CH2)1-9CO.
It is believed that halogenation of the compounds of the invention is helpful in modulating the in vivo half-life, and it may be advantageous to include halogen-substituted rings in the compounds. Indeed, various substituents may thus be included. These substituents include alkyl (1-6C), aryl (6-10C) or arylalkyl (7-16C) optionally containing 1-4 heteroatoms selected from the group consisting of halo, N, P, O, and S or may be the xe2x80x9csubstituentsxe2x80x9d halo, OR, SR, NR2, OOCR, NROCR, COR, COOR, CONR2, CF3, CN or NO2, wherein R is H or alkyl (1-6C). These substituents may also be present on the alkyl, aryl or arylalkyl or other cyclic moieties; aryl or other cyclic moieties groups may also contain alkyl substituents.
Typical heteroaromatic moieties include pyridyl, pyrimidyl, quinolyl and the like. Typical aliphatic heterocycles include, for example, piperidinyl, piperazinyl, tetrahydrofuranyl, pyranyl, and the like. Preferred embodiments of Ya and Yb include two cyclohexyl residues or a cyclohexyl and a phenyl residue.
Thus, all of the foregoing aromatic, heteroaromatic, cyclic aliphatic, and heterocyclic aliphatic moieties may be substituted or unsubstituted. Typical xe2x80x9csubstituentsxe2x80x9d include halo, OR, SR, NR2, OOCR, NROCR, COR, COOR, CONR2, CF3, CN or NO2, wherein R is H or alkyl (1-6C). They may also be substituted by alkyl (1-6C), aryl (6-10C) or arylalkyl (7-16C) optionally containing 1-4 heteroatoms selected from the group consisting of halo, N, P, O, and S which may themselves contain xe2x80x9csubstituents.xe2x80x9d Aryl residues or other cyclic residues may also be substituted by alkyl.
Preferred substituents include halo, CF3, OR, NR2, COONR2, COOR, and the like.
In the compounds of formula (1a), preferred embodiments of Ar include two phenyl moieties or a single phenyl moiety. In compounds of formula (1b), preferred embodiments of Cy include a single cyclohexyl, a cyclohexyl and phenyl moiety, or two cyclohexyl moieties.
In one set of preferred embodiments of Formula 1a Ya is two substituted or unsubstituted phenyl, Xxe2x80x2 is CH(CH2)5 or CH(CH2)4CO, Z is N, and X2 is CH2 and n2 is 0 or 1. In this embodiment, Ar is preferably an optionally substituted ring which is phenyl, pyrimidyl, especially 2-pyrimidyl or pyridyl, especially 2-pyridyl.
The invention compounds may also be supplied as pharmaceutically acceptable salts. Pharmaceutically acceptable salts include the acid addition salts which can be formed from inorganic acids such as hydrochloric, sulfuric, and phosphoric acid or from organic acids such as acetic, propionic, glutamic, glutaric, as well as acid ion-exchange resins. If the compounds contain carboxyl groups, the salts of the carboxyl groups may also be included. typical pharmaceutically acceptable salts are sodium, potassium, or calcium salts if appropriate, or salts with inorganic bases such as caffeine.
Utility and Administration
For use as treatment of human and animal subjects, the compounds of the invention can be formulated as pharmaceutical or veterinary compositions. Depending on the subject to be treated, the mode of administration, and the type of treatment desiredxe2x80x94e.g., prevention, prophylaxis, therapy; the compounds are formulated in ways consonant with these parameters. A summary of such techniques is found in Remington""s Pharmaceutical Sciences, latest edition, Mack Publishing Co., Easton, Pa., incorporated herein by reference.
In general, for use in treatment, the compounds of formulas (1a) and (1b) may be used alone, as mixtures of two or more compounds of formulas (1a) and (1b) or in combination with other pharmaceuticals. Depending on the mode of administration, the compounds will be formulated into suitable compositions to permit facile delivery.
Formulations may be prepared in a manner suitable for systemic administration or topical or local administration. Systemic formulations include those designed for injection (e.g., intramuscular, intravenous or subcutaneous injection) or may be prepared for transdermal, transmucosal, or oral administration. The formulation will generally include a diluent as well as, in some cases, adjuvants, buffers, preservatives and the like. The compounds can be administered also in liposomal compositions or as microemulsions.
For injection, formulations can be prepared in conventional forms as liquid solutions or suspensions or as solid forms suitable for solution or suspension in liquid prior to injection or as emulsions. Suitable excipients include, for example, water, saline, dextrose, glycerol and the like. Such compositions may also contain amounts of nontoxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents and the like, such as, for example, sodium acetate, sorbitan monolaurate, and so forth.
Various sustained release systems for drugs have also been devised. See, for example, U.S. Pat. No. 5,624,677.
Systemic administration may also include relatively noninvasive methods such as the use of suppositories, transdermal patches, transmucosal delivery and intranasal administration. Oral administration is also suitable for compounds of the invention. Suitable forms include syrups, capsules, tablets, as in understood in the art.
For administration to animal or human subjects, the dosage of the compounds of the invention is typically 0.1-15 mg/kg, preferably 0.1-1 mg/kg. However, dosage levels are highly dependent on the nature of the condition, the condition of the patient, the judgment of the practitioner, and the frequency and mode of administration.
Screening Methods
The compounds of the invention can be synthesized individually using methods known in the art per se, or as members of a combinatorial library. In general, Ya or Yb is coupled, along with any linking moiety, to the nitrogen of the piperazine or piperidine ring. This ring itself is generally appropriately substituted with (X2)nxe2x80x94Ar or (X2)nxe2x80x94Cy prior to this coupling. Typically, Ya(X1)n1 or Yb(X1)n1 is supplied containing a suitable electron-withdrawing leaving group, thus effecting the coupling to the ring nitrogen.
Synthesis of combinatorial libraries is now commonplace in the art. Suitable descriptions of such syntheses are found, for example, in Wentworth, Jr., P. et al. Current Opinion in Biol (1993) 9:109-115; Salemme, F. R. et al. Structure (1997) 5:319-324. The libraries contain compounds with various embodiments of R1, X1, X2, Ar, Cy, Y and Z, along with appropriate substituents. These libraries, which contain, as few as 10, but typically several hundred members to several thousand members, may then be screened for compounds which are particularly effective against a specific subtype of calcium channel. In addition, using standard screening protocols, the libraries may be screened for compounds which block additional channels such as sodium channels, potassium channels and the like.
Methods of performing these screening functions are well known in the art. Typically, the channel to be targeted is expressed at the surface of a recombinant host cell such as human embryonic kidney cells. The ability of the members of the library to bind the channel is measured, for example, by the ability of the compound in the library to displace a labeled binding ligand such as the ligand normally associated with the channel or an antibody to the channel. More typically, ability to antagonize the channel is measured in the presence of the appropriate agonist and the ability of the compound to interfere with the signal generated is measured using standard techniques.
In more detail, one method involves the binding of radiolabeled agents that interact with the calcium channel and subsequent analysis of equilibrium binding measurements including, but not limited to, on rates, off rates, Kd values and competitive binding by other molecules. Another method involves the screening for the effects of compounds by electrophysiological assay whereby individual cells are impaled with a microelectrode and currents through the calcium channel are recorded before and after application of the compound of interest. Another method, high-throughput spectrophotometric assay, utilizes loading of the cell lines with a fluorescent dye sensitive to intracellular calcium concentration and subsequent examination of the effects of compounds on the ability of depolarization by potassium chloride or other means to alter intracellular calcium levels.
The following examples are intended to illustrate but not to limit the invention.